Autoimmune diseases are classified into two types: organ-nonspecific type autoimmune diseases such as rheumatoid arthritis (hereinafter also referred to as “RA”) and organ-specific type autoimmune diseases such as ulcerative colitis. They are induced by T cells responsive to self antigens, said T cells being normally under immunological tolerance, that were activated within self tissues by certain causes to respond to self antigens, leading to continuous inflammatory reactions to thereby damage tissues. In such cases, self antigens are type II collagen that constitutes self joint or main components of the mucous membrane of the intestine, respectively.
The number of patients suffering from these diseases has been slightly increasing year by year but no effective remedies or prophylaxis have been found (Nobuo Watanabe, “Pharmacotherapy on juvenile rheumatoid arthritis”, Rheumatism, 1996, Vol. 36, No. 4, p. 670-675). Currently, for treatment of these diseases, there have been employed pharmacotherapy including administ ration of Salazopyrin, 5-aminosalycic acid, azathioprine, 6-MP, tranilast, methotrexate, cyclosporine A, or metronidazole, and administration of an excess amount of 7S-immunoglobulin; surgical therapy such as thymectomy or replacement with artificial joint; or symptomatic therapy such as nutritional therapy (Yoichi Ichikawa et al. “Study on efficacy of long-term administration of methotrexate and salazosulfapyridine on rheumatoid arthritis case” Rheumatism, 1995, Vol. 35, p. 663-670; Sadao Kashiwazaki, “Study on efficacy of combination of auranofin and methotrexate on rheumatoid arthritis”, Rheumatism, 1996, Vol. 36, p. 528-544; Takefumi Furutani et al., “Detrimental event in therapy with low dose methotiexate on rheumatoid arthritis”, Rheumatism, 1996, Vol. 36, p. 746-752; Nobuo Watanabe, Immunological Science, 1984, Vol. 9, p. 285-289 Ed. By Yuichi Yamamura, Chuzo Kishimoto, Robert A Good, “Immunodeficiency due to medicament; and Shin Totokawa et al., “Study on methotrexate therapy in rheumatoid arthritis: Seeking for strategy of more effective administration”, Rheumatism, 1997, Vol. 37, p. 681-687). However, these therapies are not eradicative but rather are disadvantageous in that they may cause severe adverse side effects due to long-term ingestion of medicaments. Thus, it is desired to develop more effective prophylactics/remedies and therapy.
SEB is one of enterotoxins (causative toxins of toxin-type food poisoning) produced by Staphylococcus aureus. SEB consists of 239 amino acid residues and its amino acid sequence is also known. The SEB molecule comprises two domains, the first domain consisting of residues 1 to 120, and the second domain consisting of residues 127 to 239. At the N-terminal of SEB, three Regions, Region 1 consisting of residues 9 to 23, Region 2 consisting of residues 41 to 53 and Region 3 consisting of residues 60 to 61, were identified that may affect binding of class II Major Histocompatibility Complex (hereinafter referred to as “MHC”) and/or binding of T cell antigen receptor (hereinafter referred to as “TCR”).
As is well known, SEB is one of bacterial superantigens (White J. et al., Cell, 1989, Vol. 56, p. 27-35). Normal antigens, being complexed with class II MHC, are recognized by TCR on T cells and this recognition is restricted to a haplotype of class II MHC molecule, called “MHC restriction”. On the contrary, superantigens are bound to class II MHC molecule irrespective of haplotype and further to a specific p chain variable region (Vβ chain) of TCR. As a consequence, T cells bound with the superantigen are transiently activated, are promoted to divide and propagate and produce inflammatory cytokines (Micusan V. V. & Thibodean J., Seminars in Immunology, 1993, Vol. 5, p. 3-11).
When a superantigen is intravenously or intraperitoneally administered to newborn mice, a subpopulation of T cells having VβTCR responsive to the superantigen is eliminated so that said mice become non-responsive to said antigen, i.e. immunological tolerance. On the other hand, when SEB is administered to adult mice, the condition where T cells bearing VβTCR that binds to the superantigen become non-responsive to further stimulation with the superantigen, i.e. anergy, is induced, to thereby cause immunological tolerance. Such features of a superantigen are distinct from the normal antigen recognition. With the ability to induce immunological tolerance in T cells bearing the specific VβTCR, SEB is suggested to be applicable for prevention or treatment of certain immunopathy, in particular, type I allergic diseases or autoimmune diseases. Indeed, it is reported that SEB administration to a system of disease model mice allowed for inhibition of onset of said disease.
Kim C. et al. reported that lupus nephritis in MRL/lpr mice, model mice of Systemic lupus erythematosus (hereinafter referred to as “SLE”), could be suppressed by previously administering SEB (Kim C. et al., Journal of Experimental Medicine, 1991, vol. 174, p. 1431-1437). Rott O. et al. also reported that SEB was previously administered to a system of Experimental Allergic Encepharomyelitis (hereinafter referred to as “EAE”) to induce immunological tolerance in T cells bearing the VpβTCR responsive to SEB to thereby suppress the disease (Rott O. et al., International and National Immunology, 1992, Vol. 4, No. 3, p. 347-353). These results suggest a possibility that SEB may be used as a vaccine to allow for prevention of specific autoimmune diseases.
However, in these experiments, SEB was administered intravenously or intraperitoneally with a dose of as much as around 100 μg per animal. With such a high dose, an extent of pathogenicity not disregarded will inevitably be introduced to mice and antigenicity and immunogenicity are also problematic. In particular, as described above, a superantigen, when administered at a large amount, will induce transient activation of the subpopulation of T cells or antigen-presenting cells to invite acceleration of inflammatory cytokine production, resulting in the acute inflammatory condition within the living body. Besides, in case of human, Kuwahata et al. reported that an anti-SEB antibody is present in blood from almost 100% of children of more than the school age and an anti-IgA antibody is detected in about 50% of the children from analysis of saliva et al. (M. Kuwahata et al., Acta Pediatrica Japonica, 1996, 38, p. 1-7). Origuchi et al. also demonstrated that a level of IgM-type anti-SEB antibody is significantly high in serum from patients suffering from rheumatism (Origuchi et al., Annals of the Rheumatic Disease 1995, 54, p. 713-720). Moreover, Nishi et al. revealed that a major epitope of an anti-SEB antibody in human serum is located at a C-terminal of SEB and an antibody against said C-terminal region is a neutralizing antibody to SEB (Jun-Ichiro Nishi et al., The journal of Immunology, 1997, 158, p. 247-254). This implies that, when SEB is administered to human, SEB will be neutralized for its biological activity by the antibody and eliminated from the living body. Thus, Nishi et al. constructed a mutant SEB lacking the major epitope at the C-terminal using the genetic engineering technique. However, the thus prepared modified SEB could only be expressed in an insoluble form to hamper thorough assessment and analysis. Also said modified SEB could not cope with stable supply of medicine.
To tackle the various problems in association with administration of a large amount of a superantigen, the present inventors provided a measure for effectively inducing immunological tolerance by orally administering a highly purified SEB in a dose not inducing pathogenicity successively for a long period of time (Japanese Patent Publication No. 110704/1997) and constructed a modified SEB and a derivative thereof through molecular alteration of SEB in which inherent toxicity of SEB is reduced while its preventive/therapeutic effect for immunopathy is maintained to prove utility of SEB (WO99/40935).